The present invention relates to a scroll compressor, and more particularly, it relates to a scroll compressor improving sealability between a fixed scroll and a movable scroll and suppressing internal leakage.
A scroll compressor described in Japanese Patent Laying-Open No. 6-330864 (1994) is now described as an example of a conventional scroll compressor.
Referring to FIG. 8, a movable scroll 103 and a fixed scroll 102 are supported on an upper portion in a casing 101 of the scroll compressor. Movable scroll teeth 132 project from an end plate 131 of the movable scroll 103. Fixed scroll teeth 122 project from an end plate 121 of the fixed scroll 102. The movable scroll teeth 132 and the fixed scroll teeth 122 fit with each other thereby forming a compression chamber.
A suction port 180 for introducing refrigerant gas fed from a suction pipe 107 into the compression chamber is provided on the outer peripheral portion of the fixed scroll 102. A discharge port 123 for discharging the refrigerant gas compressed to a high-pressure state is formed around the center of the fixed scroll 102.
A motor 104 is provided on a lower portion in the casing 101. A drive shaft 141 extending from the motor 104 is supported by a bearing housing 105 fixed to the lower portion of the movable scroll 103. A boss 133 provided on the end plate 131 of the movable scroll 103 is engaged with an upper end portion of the drive shaft 141.
A back pressure chamber 109 is formed between the bearing housing 105 and the movable scroll 103. A high pressure (discharge pressure) acts on the back pressure chamber 109. A seal ring 170 is provided between the movable scroll 103 and the bearing housing 105.
This seal ring 170 seals the back pressure chamber 109 of a high pressure and a space of a low pressure (suction pressure) provided with the movable scroll 103 and the fixed scroll 102. Therefore, it follows that the discharge pressure acts on a region of the back surface of the end plate 131 of the movable scroll 103 located inside the seal ring 170 and the suction pressure acts on another region of the back surface located outside the seal ring 170.
The end plate 121 of the fixed scroll 102 is provided with a relief port 110 and a relief valve 111 for discharging the refrigerant gas from the compression chamber in the process of compression into a discharge chamber 101A in order to prevent over-compression.
A cover body 124 covering the upper side of the discharge port 123 is mounted on the fixed scroll 102 with fixing bolts. The cover body 124 is coupled to a support plate 106 fixed to the upper portion in the casing 101. The support plate 106 is provided with a communication hole 161 communicating with the discharge port 123.
A communication path 101C connects the discharge chamber 101A of the casing 101 communicating with the communication hole 161 with a space 101B located below the bearing housing 105. The space 101B communicates with a discharge pipe 108 for discharging the refrigerant gas of a high pressure from the casing 101.
Operation of the aforementioned scroll compressor is now described.
Following rotation of the motor 104, the movable scroll 103 revolves with respect to the fixed scroll 102 so that the compression chamber formed by the movable scroll teeth 132 and the fixed scroll teeth 122 spirally contractedly moves from the outer peripheral portion toward the central portion.
Thus, the refrigerant gas of a low pressure fed into the compression chamber from the suction pipe 107 through the suction port 180 is compressed to a high-pressure state. The high-pressure refrigerant gas is discharged from the discharge port 123 and flows into the space 101B through the communication hole 161, the discharge chamber 101A and the communication path 101C. The discharge pipe 108 discharges the refrigerant gas flowing into the space 101B from the casing 101.
The pressures acting on the end plate 131 of the movable scroll 103 in the aforementioned operations are now described. The pressure of the fluid in the compression chamber as well as a back surface pressure act on the end plate 131. FIG. 9 typically shows pressure distribution in the compression chamber and pressure distribution on the back surface with respect to positions of the end plate 131.
As hereinabove described, the compression chamber spirally contractedly moves from the outer peripheral portion toward the central portion. Therefore, the pressure of the compression chamber increases from the outermost peripheral portion in a suction process toward a portion in a discharge process through a portion in the process of compression.
Therefore, the portion of the compression chamber in the suction process has the lowest pressure, i.e., a suction pressure Ps, and the portion in the discharge process has the highest pressure, i.e., a discharge pressure Pd. The portion of the compression chamber in the process of compression exhibits a pressure Pm between the suction pressure Ps and the discharge pressure Pd.
Thus, it follows that force (separating force) for separating the movable scroll 103 from the fixed scroll 102 acts on the end plate 131 of the movable scroll 103 on the basis of the aforementioned pressures.
On the other hand, the discharge pressure Pd acts on the region of the back surface of the end plate 131 located inside the seal ring 170 while the suction pressure Ps acts on the region located outside the seal ring 170, as hereinabove described.
Thus, it follows that force (pressing force) for pressing the movable scroll 103 against the fixed scroll 102 acts on the end plate 131 of the movable scroll 103 oppositely to the separating force, on the basis of the aforementioned pressures.
When the scroll compressor is operated at a standard operating pressure ratio, the pressures are distributed as shown in FIG. 9. In this case, therefore, sufficient pressing force is attained as compared with the separating force for preventing separation of the movable scroll 103 from the fixed scroll 102. The scroll teeth 122 and 132 come into close contact with the end plates 121 and 131 respectively, to be capable of suppressing internal leakage.
The operating pressure ratio, depending on a refrigerating cycle of the scroll compressor including an evaporator and a condenser, is obtained by dividing the discharge pressure Pd depending on a condensing pressure by the suction pressure Ps depending on an evaporating pressure.
At the standard operating pressure ratio, this value is at the same level as a designed pressure level decided by the scroll teeth 122 and 132, more specifically in the range of about 2 to 5.
As hereinabove described, sufficient pressing force is attained as compared with the separating force to be capable of suppressing internal leakage when the scroll compressor is operated at the standard operating pressure ratio.
When the scroll compressor is operated at a low operating pressure ratio of not more than about 2, however, the following problem arises: Such an operating pressure ratio is less than the designed pressure ratio. More specifically, the suction pressure Ps is relatively increased as compared with the discharge pressure Ps or the discharge pressure Pd is relatively reduced as compared with the suction pressure Ps at such an operating pressure ratio. In this case, therefore, the pressure of the compression chamber in the process of compression may exceed the reduced discharge pressure.
Pressure distribution in the compression chamber and pressure distribution on the back surface with respect to the positions of the end plate 131 with such a low operating pressure ratio are now described. As shown in FIG. 10, the portion of the compression chamber in the suction process exhibits the lowest pressure, i.e., the suction pressure Ps, while the portion in the process of compression exhibits the highest temperature, i.e., the pressure Pm. The portion in the discharge process exhibits the discharge pressure Pd between the suction pressure Ps and the pressure Pm. It follows that separating force acts on the end pressure 131 on the basis of these pressures.
On the other hand, the discharge pressure Pd acts on the region of the end plate 131 located inside the seal ring 170 as back pressure force, while the suction pressure Ps acts on the region located outside the seal ring 170. It follows that pressing force acts on the end plate 131 on the basis of these pressures.
Comparing the separating force with the pressing force, the former is insufficient with respect to the latter since the discharge pressure Pd is lower than the pressure Pm of the portion in the process of compression. Therefore, the scroll teeth 122 and 132 may not be in close contact with the end plates 121 and 131 respectively but internal leakage may take place from the high-pressure side toward the low-pressure side of the compression chamber.
When the pressure in the portion of the compression chamber in the process of compression exceeds a prescribed level (over-compression) in the aforementioned scroll compressor, the relief valve 111 can be open for discharging the refrigerant gas from the compression chamber into the discharge chamber 101A through the relief port 110. Thus, it follows that the pressure in the portion of the compression chamber in the process of compression is reduced to about the discharge pressure Pd.
In the portion of the compression chamber following (outside) the portion communicating with the relief port 110, however, the pressure is higher than the suction pressure Ps. Although the pressure of the portion of the compression chamber communicating with the relief port 101 is reduced to about the discharge pressure Pd, therefore, the pressing force is still so insufficient with respect to the separating force that internal leakage may take place.
The present invention has been proposed in order to solve the aforementioned problem, and an object thereof is to provide a scroll compressor capable of attaining sufficient pressing force with respect to separating force and reducing internal leakage.
A scroll compressor according to a first aspect of the present invention comprises a fixed scroll and a movable scroll, a suction port, a discharge port, an unloader part, control means and a first back pressure chamber. The fixed scroll and the movable scroll form a compression chamber. The suction port feeds a fluid into the compression chamber. The discharge port discharges the fluid compressed in the compression chamber. The unloader part guides the fluid from the compression chamber in the process of compression toward the suction port. The control means operates the unloader part. The first back pressure chamber is provided on the back surface of either the fixed scroll or the movable scroll for receiving the fluid, having a discharge pressure, discharged from the discharge port. The control means detects, calculates or predicts a suction pressure and the discharge pressure, compares separating force for separating the fixed scroll and the movable scroll from each other with pressing force for pressing one of the scrolls against the other scroll on the basis of the detected, calculated or predicted suction pressure and discharge pressure and operates the unloader part when the pressing force is insufficient or to be insufficient with respect to the separating force for releasing the fluid from the compression chamber in the process of compression toward the suction port.
When the scroll compressor is operated at a low operating pressure ratio and separating force is to exceed pressing force due to over-compression or the like, for example, the control part detects this and operates the unloader part for guiding the fluid from the compression chamber in the process of compression toward the suction port. Thus, relatively sufficient pressing force is attained due to reduction of the separating force also when the pressing force is reduced, so that the compression chamber can be inhibited from internal leakage. Further, the over-compression can be relaxed.
Preferably, the control means of the scroll compressor calculates the discharge pressure and the suction pressure from the temperatures of the fluid flowing through an evaporator and a condenser connected between a discharge pipe delivering the discharged fluid and a suction pipe receiving the fluid respectively on the outside of a casing respectively.
In this case, an evaporating pressure and a condensing pressure are uniquely obtained from an evaporating temperature obtained from the temperature of the fluid flowing through the evaporator and a condensing temperature obtained from the temperature of the fluid flowing through the condenser respectively. The evaporating pressure and the condensing pressure are substantially equal to the suction pressure and the discharge pressure respectively. Thus, the suction pressure and the discharge pressure can be readily obtained by measuring the temperature of the fluid flowing through the evaporator and the temperature of the fluid flowing through the condenser.
Preferably, the unloader part of the scroll compressor has a first switching part provided on an intermediate portion of a first passage connecting the compression chamber in the process of compression with a region located on the side of the suction port for opening/dosing the first passage with the fluid of the discharge pressure or the fluid of the suction pressure, for opening the first switching part by guiding the fluid of the suction pressure to the first switching part and closing the first switching part by guiding the fluid of the discharge pressure to the first switching part.
In this case, the first switching part can be readily opened/closed by switching the fluid of the discharge pressure and the fluid of the suction pressure through the pressure of the fluid.
More preferably, the scroll compressor further comprises a second back pressure chamber receiving the fluid of the discharge pressure in a decompressed state on the back surface of the scroll provided with the first back pressure chamber.
In this case, the fluid of the discharge pressure is decompressed so that the pressure in the second back pressure chamber reaches a level between the discharge pressure and the suction pressure. Thus, more sufficient pressing force is attained as compared with the case where the second back pressure chamber is at the suction pressure, so that internal leakage can be effectively suppressed. Further, the pressing force is reduced when the scroll compressor is operated at a general operating pressure ratio as compared with the case of setting the first and second back pressure chambers entirely to the suction pressure, and hence one of the scrolls is not excessively pressed against the other scroll.
Preferably, the scroll compressor further comprises a sealing member sealing the first back pressure chamber and the second back pressure chamber, and the fluid of the discharge pressure is decompressed by flowing from the first back pressure chamber into the second back pressure chamber through a clearance in the vicinity of the sealing member.
In this case, the fluid can be readily decompressed without requiring a complicated mechanism.
More preferably, an electric motor for driving the movable scroll is a variable-speed electric motor.
In this case, defrost operation, for example, can be ended in a short time by increasing the rotational frequency of the electric motor.
Preferably, the scroll compressor further comprises a relief port for directly guiding the fluid from the compression chamber in the process of compression to a region located on the side of the discharge port and a relief valve provided on an intermediate portion or the outlet of the relief port for opening the relief port when the pressure in the compression chamber in the process of compression exceeds the pressure on the side of the discharge port.
When the operating pressure ratio is extremely small, over-compression may take place despite operation of the unloader part. In this case, the fluid is released toward the region located on the side of the discharge port from the compression chamber causing over-compression, so that the over-compression can be relaxed.
A scroll compressor according to a second aspect of the present invention comprises a fixed scroll and a movable scroll, a suction port, a discharge port, an unloader part and a first back pressure chamber. The fixed scroll and the movable scroll form a compression chamber. The suction port sucks a fluid into the compression chamber. The discharge port discharges the fluid compressed in the compression chamber. The unloader part guides the fluid from the compression chamber in the process of compression toward the suction port. The first back pressure chamber is provided on the back surface of either the fixed scroll or the movable scroll for receiving the fluid, having a discharge pressure, discharged from the discharge port. The unloader part includes a switching part opened/closed by working the discharge pressure on one side of a piston part while working a suction pressure and elastic force on another side, for guiding the fluid from the compression chamber toward the suction port when the discharge pressure is smaller than the suction pressure and the elastic force.
When the scroll compressor is operated at a low operating pressure ratio and the discharge pressure is reduced below the suction pressure and the elastic force due to over-compression or the like, the switching part is automatically open to operate the unloader part thereby guiding the fluid from the compression chamber in the process of compression toward the suction port. Thus, relatively sufficient pressing force is attained due to reduction of separating force also when the pressing force is reduced, so that the compression chamber can be inhibited from internal leakage. Further, the over-compression can be relaxed.
Preferably, the scroll compressor further comprises a second back pressure chamber provided on the back surface of the scroll provided with the first back pressure chamber for receiving the fluid of the discharge pressure in a decompressed state.
In this case, the fluid of the discharge pressure is decompressed so that the pressure in the second back pressure chamber reaches a level between the discharge pressure and the suction pressure. Thus, more sufficient pressing force is attained as compared with the case where the second back pressure chamber is at the suction pressure, so that internal leakage can be effectively suppressed. Further, the pressing force is reduced when the scroll compressor is operated at a general operating pressure ratio as compared with the case of setting the first and second back pressure chambers entirely to the suction pressure, and hence one of the scrolls is not excessively pressed against the other scroll.
Preferably, the scroll compressor further comprises a sealing member sealing the first back pressure chamber and the second back pressure chamber, and the fluid of the discharge pressure is preferably decompressed by flowing from the first back pressure chamber into the second back pressure chamber through a clearance in the vicinity of the sealing member.
In this case, the fluid can be readily decompressed without requiring a complicated mechanism.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.